The purpose of this study was to examine the effects of raising grandchildren on middle-elderly women’s mental health. The study looked at two aspects of middle-elderly women’s mental health, satisfaction with life and depression. It also examined if the association between grandchild-rearing and mental health was mediated by the satisfaction in grandmother-adult child relationship. In this study, middle-elderly women raising their grandchildren are defined as women who have experience raising grandchildren under age 10. The final sample of 2,744 female respondents over 50 with more than one child was selected from 7,920 who were tracked until the third wave of KLoSA(Korean Longitudinal Study of Aging). Measured variables were grandchild-rearing experience, mental health (satisfaction with life and depression), and satisfaction with the relationship with their adult children. SPSS WIN 21.0 program was used for analysis, and multiple regression analysis was used to examine whether raising grandchildren affects middle-elderly women’s mental health. Also, Sobel test was conducted after performing hierarchical multiple regression analysis to find out if satisfaction in the relationship with adult children mediates the association between grandchild-rearing and middle-elderly women’s mental health. The results of this study are as follows: First, raising grandchildren had an impact on middle-elderly women’s mental health in terms of satisfaction with life. In other words, grandchild-rearing caused a higher level of life satisfaction in middle-elderly women, while no evidence was found to prove its impact on depression. Second, the satisfaction in a grandmother-adult child relationship ediated between grandchild-rearing and life satisfaction. In other words, middle-elderly women’s level of life satisfaction was increased by raising their grandchildren, with indirect effects from satisfaction in their relationship with their adult child.